Steel purification vacuum method



Aug., Il?, 1965 R. smwfm@ @115ML ymg@ STEEL PURIFICATION VACUUM METHODFiled Aug. 6, 1962 5 Sheets-Sheet l Aug- 17, 1955 y R. sPoLDERs ETAL3,201,226

STEEL PURIFICATION VACUUM METHOD Filed Aug. 6, 1962 5 Sheets-Sheet 2Aug. 17, 1965 R. sPoLDERs ETAL STEEL PURIFICATION VACUUM METHOD 5Sheets-Sheet 3 Filed Aug. 6, 1962 .inve/7M@ @MAJ f, ffff/Qf Aug 17 1955R. sPoLDERs ETAL 3,201,226

STEEL PURIFICATION VACUUM METHOD Filed Aug. 6, 1962 5 Sheets-Sheet 4.Im/@ninfa Hw@ lau/Yun,

ug- 17, l965 R. sPoLDERs ETAL 3,201,226

STEEL PURIFICATION VACUUM METHOD Filed Aug. 6, 1962 5 Sheets-Sheet 5United States, Patent O 3,201,226 STEEL PURIFIQAHN VACUUM METHD RudolfSpolders, Bochum, Wilhelm Breung, Hattingen, and Heinz Pieper, Bochum,Germany, assignors to Ruhrstahl Hiittenwerhe Aktiengesellschaft, Essen,Germany Filed Aug. 6 1962, Ser. No. 214,963 Claims priority,implication` Germany, Feb. 27, 1957, R 20,644; Mar. Z9, 1959, R 25,203,R 25,204 l Claims. (Cl. 75-49) This is a continuation-in-part of ourapplication Serial No. 16,754 filed Mar. 22, 1960, and now US. PatentNo. 3,060,015, granted Oct. 23, 1262, which application, in turn, is acontinuation-in-part of our application Serial No. 717,756, filed Feb.26, i958, and now abandoned.

The present invention relates to steel purification and moreparticularly, it relates to a method for purifying molten steel by meansof gases.

It is well known that steel, as it comes from the furnace or converter,contains considerable quantities of occlusions `including gases whichexert a harmful eifect and the passage of which through the bath ofmolten steel is rendered difiicult or prevented due to the ferrostaticpressure of the molten steel.

It has been attempted to facilitate the passage of undesirable gasesthrough and out of the molten `steel by passing argon through the bodyof molten steel. The argon while not reacting with the steel serves toflush out desirable gases. However, the large quantities of argonrequired forthis purpose are frequently not available and, in any event,malte this process uneconomical.

It is therefore an object of the present invention to provide aneffective and economical method for the removal of undesirable matterfrom molten steel.

It is another object of the present invention to provide a methodwhereby particularly hydrogen can be removed from molten steel in aneconomical and simple manner.

Gther objects and advantages of the present invention will becomeapparent from a further reading of the description and of the appendedclaims.

With the above and other objects in view, the present inventioncontemplates in a method of purifying steel, the steps of subjecting amass of molten steel to a partial vacuum blowing a first oxidizing gasinto the lower portion of the mass of molten steel, and simultaneouslyblowing a second non-oxidizing or reducing gas into the interior of themass of molten steel at a point located above the lower portion of themass of molten steel, while maintaining the partial vacuum.

According to a preferred embodiment of the present invention, the samecomprises in a method of purifying molten steel, the steps of blowinghydrogen gas into the bottom portion of a mass of unkilled molten steel,and blowing into the interior of the mass of molten steel at a pointlocated above the bottom portion thereof a second gas selected from thegroup consisting of `argon and carbon monoxide.

It has been found that a molten steel bath can be purged easily of alarge proportion of undesirable gases by blowing through the moltensteel either carbon dioxide or carbon monoxide or a mixture of these twogases. It may be assumed that the following reactions odour when carbondioxide is blown through the molten steel:

lt is believed that the above assumption will facilitate theunderstanding of the present invention, however, the present inventionis not based on or dependent on the accuracy of the reaction describedabove.

It has been found that frequently best results are obtained by using aquantity of 5 cubic meters of carbon dioxide calculated at atmosphericpressure per 1 metric ton of molten steel. When using 5 cubic meters ofcarbon dioxide for l metric ton of molten steel the decarbonization willamount to 0.1 kilogram per ton of steel.

When carbon monoxide is blown through the molten steel, decarbonizationof the same does not take place but only a flushing or purging effect.

Due to the fact that the reaction of carbon dioxide within the moltensteel is an endothermic reaction and since heat is also withdrawn by theblowing process itself, it has been found advantageous to preheat thegases, be it carbon dioxide or carbon monoxide or a mixture of the same,in per se known manner prior to introduction of the gases into themolten steel. In many cases it has been found particularly advantageousto burn Carbon monoxide with oxygen so as to transform all or part ofthe carbonmonoxide into carbon dioxide and to introduce the thus-formedhot reaction gas into the steel bath.

This latter method also affords the opportunity to introduce the gasinto the steel bath at optimum temperature. The carbon monoxide used forthis: purpose may be for instance produced in a coke generator operatedwith oxygen and carbon dioxide, such as is described in the copendingpatent application Serial No. 682,256, Div. 59, or the carbon monoxidemay also be formed by decomposition of synthetic gas, or in any othersuitable manner.

lt has been found particularly advantageous according to the presentinvention to combine `the gas treatment of the molten steel bath with avacuum treatment of the same. Heat consuption in a vacuum chamber usedfor this purpose is considerable and it is therefore desirable topreheat the gas which is to be blown through the molten steel in thevacuum chamber. A further economy with respect to the heating of thevacuum chamber can be achieved by introducing within the chamber intothe area adjacent to the upper surface of the liquid steel body aquantity of oxygen suihcient to burn carbon monoxide emanating at thesurface of the molten steel so that the thereby formed combustion heatcan be utilized for the heating of the vacuum chamben Per t0n of moltensteel about l0 cubic meters of carbon monoxide calculated at atmosphericpressure will become available and consequently the heat provided byoxidation of carbon monoxide near the surface of the molten steelbath'will amount per ton of molten steel to about the following:

(5) Q (heat) :10X 302G=3020 .Kcal

The novel features which are considered as characteristic for theinvention are set forth in particular in the appended claims. Theinvention itself, however, both as to its construction and its method ofoperation, together with additional objects and advantages thereof, willbe best understood from the following description of specic embodimentswhen read in connection with the accompanying drawings, in which:

FIG. 1 is au elevational View in cross section of an embodiment of thedevice of the present invention;

FIG. 2 is a cross section through the device illustrated in FIG. 1 takenalong the line Il-II;

FIG. 3 is an elevational view in cross section of an other embodimentofthe device of the present invention; FIG. 4 is an elevational view incross section of yet another embodiment of the device according to thepresent invention;

FIG. 5 is an elevational View in cross section of a sa furtherembodiment of the device according to the present invention; and

FIG. 6 is an elevational view in cross section of a still anotherembodiment of the device according to the invention.

Referring now to the drawings, and particularly to FIGS. 1-3, container1 adapted to receive molten steel is shown carrying in its bottomportion removable tuyere block 2 and laterally spaced therefrom stoppernozzle 3. Underneath container l, a blast box d of circular horizontalcross section is shown towards which burner 5 extends in a directiontangential to the inner circular wall lof the blast box d. Oxygen isintroduced into burner 5 through conduit d, and carbon monoxide throughconduit portion 7. Within the blast box d combustion of the carbonmonoxide t-o carbon dioxide takes place. Thus, blast box 4 fulfills thefunction of a combustion chamber. Blast box i may also be additionallyprovided with a conduit for introducing carbon dioxide into the same.However, it is also possible to introduce carbon dioxide jointly witheither the oxygen or the carbon monoxide, or to use an excess of carbonmonoxide relative to the quantity of oxygen. The individual nozzles ofthe tuyere block preferably have a dia ieter of about l rnm. in order toprevent liquid steel after completion of the introduction of gas to passthrough the nozzles into the combustion chamber or blast box. lf thediameter of the nozzle is chosen sufficient-ly small, steel willpenetrate into the same only for a short distance and will thensolidify. The tuyere blocl: is then to be removed after each treatmentof a batch of molten steel and after the treated steel has been drawnoir".

As Will be explained in detail below, it is particularly advantageous toadmix a gaseous halogen or halogen compound to the carbon monoxide orcarbon dioxide gas prior to blowing the same through the molten steel.For in troduction of a halogen or a vaporized halogen compound, it issometimes advantageous to provide an additional conduit communicatingwith blast box Il. Evaporation or gasification of suitable halogencompounds is known per se and can be achieved without diihculties.

As illustrated in FlG. 3, a hood 8 is superposed over container 1 so asto form a vacuum chamber. It is of course necessary that hood S andcontainer ll are airtightly connected. Conduit 9 leads to a suitablevacuum pump provided with a cooling device, and lance llt? serves forintroducing oxygen into the vicinity of the upper level of molten steelwithin container 1, i.e. into the area where carbon monoxide emanatesfrom the molten steel. Thereby it is achieved that the carbon monoxideis ioxidized to carbon dioxide, freeing a considerable amount of heatand thus improving the heat economy of the entire process.

A preferred embodiment of the present invention will he best understoodin connection with FG. 4 of the drawing. The purication of the steelbath is carried out according to FIG. 4 under vacuum and withintroduction of two diiferent gases which are introduced verticallyspaced from each other. This can be accomplished in a modilication ofthe apparatus illustrated in FG. 1, and including the followingfeatures.

A cover 8 is superposed upon container l closing the same. Cover S isformed with conduit 9 communicating with a means for producing a partialvacuum. Lance l@ extends into the container and terminates therein at apoint upwardly spaced from the gas distributing means 2 located in thebottom of container ll.

Reference numeral 11 indicates a sight glass and reference numeral 12 aconventional arrangement for preventing splashing molten steel fromentering into conduit 9 leading to the vacuum pump or the like.

With an apparatus such as illustrated in FIG. 4, and described above, itis possible to introduce at least two gases of different compositioninto the molten metal while simultaneously maintaining a partial Vacuumin the apparatus. Introduction of the two gases is carried tout at or inthe vicinity of the bottom of the container and at a level which issubstantially higher than the container bottom. In many cases, it hasbeen found to be particularly advantageous to introduce into the moltensteel through the bottom of the container an oxidizing gas, and throughthe lance at the higher level a deoxidizing `or neutral gas. On theother hand, particularly in the case of unkilled steel, a reducing gassuch as hydrogen gas may be introduced through the bottom of thecontainer and a substantially neutral gas such as argon or carbonmonoxide through the lance at the higher level. The neutral gas which isintroduced through a lance may also consist fully or in part ofvaporized or gasiiied ha-logens or halogen compounds.

After treatment by introduction of anl oxidizing gas has been completed,it is sometimes desirable to introduce through the bottom distributingplate 2 a reducing gas without introducing a second gas through thelance during this last stage of the process.

The apparatus illustrated in FIGS. 5 and 6 is particu larly well suitedfor providing a partial Vacuum without requiring tight closing of theentire container top.

According to the embodiment of FIGS. 5 and 6, a hood is partiallylowered into the container so that the lowermost preferably outwardlyaring portion of the hood will be situated below the upper level ofVmolten metal in the container. This allows a convenient and flexiblearrangement of the lance, as well as gas introduction and gas withdrawaltowards the vacuum producing means, without requiring the placing of anair-tight cover member on the top of the container.

As shown in FIGS. 5 and 6, the lower portion of hood l2 extendsdownwardly below level lo of the molten steel in container 4. Due to thedownwardly Haring coniiguration fof lower portion l1 ,of hood 12, gaslosses will not occur to any appreciable extent. Gas will be withdrawnfrom the molten metal towards the partial vacuum maintained in hood 12.Due to the partial vacuum therein, the upper level 17 of molten metalwithin hood 12 will be higher than the upper level 16 of molten metaloutside hood 12. Hood i2 is removably kept in the indicated position byconventional means not shown in the drawing. Conduit 1S connects theinterior of hood 1.2 with vacuum-producing means such as a vacuum pump(not shown). Gas is introduced into the molten metal vrithin thecontainer by means of lance 13.

The embodiment illustrated in FIG. 6 dilfers from what is shown in FlG.5 by additionally providing means for introducing gas through the bottomof the container, similar to those shown in FIG. l; by including inVhood 12 an arrangement l@ for preventing splashing metal from reachingvacuum conduit l5, and by arranging sight glass t7 in the upper portionof hood 12. Tuyere block 2 is replaceable and may be removed after hood12 has been raised, the container has been tilted and the molten metalhas been poured. In combustion chamber 4, a mixture of a combustible gassuch as carbon monoxide (which is introduced through nozzle 7) andoxygen (introduced through conduit d) may be burnt and the thus formedhot combustion gas introduced into the container through distributor 2.ln this manner, Very hot carbon dioxide gas penetrates from the bottomof the container through the molten steel and passes into daring hoodportion 1l, so that separate heating means for the steel bath will notbe required. Additionally, a similar or different gas may be introducedthrough lance 13. lt is of course possible to introduce a great varietyof gases through lance i3 and tuyere block 2 depending on the specificrequirements of the melt. s Y

As stated above, it is possible to introduce jointly with the purginggas consisting of carbon monoxide or carbon dioxide or a mixture ofcarbon monoxide and carbon dioxide, a halogen or vaporized halogencompound into the molten metal bath. Thereby, it is achieved that due tothe intermediary reactions between the halogen and the hydrogen gascontained in the steel bath, the gaseous hydrogen is removed from thesteel bath to a very considerable extent. For practical purposes,chloride and fluorine are preferred as halogens for the present process,particularly in view of the higher costs of bromine and iodine.

A great number of halogen compounds can be advantageously used inaccordance with the present invention. Particularly good results areobtained by using aluminum chloride or'aluminum fluoride as the halogencompound and it has also been found that carbon tetrachloride isparticularly elfective since it is relatively easy to saturate thepurging gas with any desired dosage of carbon tetrachloride andconsequently optimum concentration of the carbon tetrachloride for anygiven operating conditions can easily be maintained. However, otherhalogenized hydrocarbons such as hexachlorobenzene have also beenadvantageously used. All of these` halogen-supplying gases or Vaporizedsubstances can be used either alone or as a mixture of several of thesame.

The following examples are given as illustrative of the process ofthepresent invention, the invention however not being limited to thespecific details of the examples.

Example II Steel Type: St 37 m Si Standard Analysis:

C, 0.10-0.14 Si, 0.15-0.30 Mn, 0.40-0.50 P upto 0.035 t S up to 0.035Batch Analysis: C, 0.13 Si, 0.20

Mn, 0.4-8 P, 0.026

Temperatures Prior to treatment, 1620 C.

After treatment, 1590 C. Ti'eating Gas:` CO, 4.0 m.3/t. steel TreatingTime: 12 minutes Gas Pressure: 2.2-2.4 atmospheres excess pressureHydrogen Content:

Prior to treatment, 8.0 cm3/100 g. steel` After treatment, 4.8 cm/ 100g. steel 6 Example III Steel Type: SII shipbuilding plate StandardAnalysis:

C, 0.14-0.17 Si, O15-0.30 Mn, G50-0.60 P upto 0.045 S up to 0.045 BatchAnalysis:

C, 0.17 Si, 0.22 Mn, 0.51 P, 0.038 S, 0.028 Temperatures 2 Prior totreatment, 1610a C. After treatment, 1585 C. Treating Gas: CO2-CCL, GasConsumption:

CO2, 2.54- m.3/t. of steel CC14, 0.043 l./t. of steel Treating Time: l2minutes Gas Pressure: 2.2-2.4 atmospheres excess pressure HydrogenContent:

Prior to treatment, 8.3 cm.3/ g. steel After treatment, 3.6 cm/ 100 g.steel In all examples, gas volumes are given vat atmospheric pressure.

The puriiication obtained according to the present invention can beclearly seen by comparing the hydrogen content of the steel prior andafter treatment. Hydrogen content in all cases was determined on steel.samples taken from the treating vessel. Furthermore, the viscosity ofthe treated steel was lower thus facilitating casting of the same.

This was true with the steel `as before mentioned with an oxide contentof 0.04% and hydrogen content of 7-8 cm.3/\100 g. steel. After blowingof 1'80 m CO with 2% Cl the temperature was changed from 1600 C. to 1590C., the oxide content was @O15-0.02% and hydrogen content 3.5 cm3/1100g. steel.

The degree of vacuum applicable in the process of the invention may bevaried within wide ranges. Although it is poss-ible to apply a vacuum,eg. of 50-0.1 mm. Hg and less, it may be preferred to apply a vacuum notfar from atmospheric pressure (S0-400 mm. Hg under atmosphericpressure), i.e. the pressure within the vessel may be between about700-300 mm. Hg.

The amount of halogen, e.g. chlorine, may range `from .about 2 to 5% ofthe gas or gas mixture applied. When using halogen compounds the amountsof said compounds may be calculated so that the `amount of halogen, e.g.chlorine, contained in said compounds would constitute about 2-5% of thegas or gas mixture. This is true also when 2 or more halogen or halogencompounds or mixturcs -ot halogen and halogen compound are used.

Besides, the proportions of CO and CO2 may be varied `as desirable forthe special conditions. Itis preferred to burn off a part of CO to CO2to raise the temperature of the gas mixture. So, e.g. a mixture withabou-t 50% CO and 50% CO2 with an 4addition of vaporized aluminumchloride (7 kg.) was very effective. A similar mixture was prepared with45% CO and 55% CO2; with an addition of carbon tetrachloride (6 kg).

Introduction of suitably preheated gas will prevent any `appreciabledrop of the temperature of the steel bath dur-ing the above describedpurification process.

Example I V Molten steel, ltreated and finished in conventional mannerin an electric furnace, was introduced into container 1 of the apparatusshownin FIG. 4.` Container 1 had a capacity of 30 tons and thecomposition of the steel was as follows:

Percent C 0.35 Si 0.27 Mn 0.59 S 0.017 P 0.009

After introducing the steel into container 1, the container was closedby superposing thereon cover 8 holding lance 10 so that the free end oflance 10 was located about in the center of the bath of molten steel. Incombustion chamber 4, a hot gas consisting of 90% carbon dioxide .and10% carbon monoxide was produced by combustion of carbon -monoxide withoxygen. Production of this gas was so arranged that a total quant-ity ofabout 25 liters of hot gas were introduced into container for each tonof molten steel. Through the lance, hydrogen gas was blown into themolten steel in an amount of liters per ton of steel. Pressure reductionwas carried out so that after about three minutes Ia residual pressureof 2 mm. mercury was reached and this residual pressure was thenmaintained during the entire treating period which lasted a total offifteen minutes.

Thereafter, atmospheric pressure rwas restored, cover `and lance 10 wereremoved and it was found that the above-descri bed two-gasvacuum-treatment had resulted in `a reduction of the oxygen content ofthe steel by about 50%, the hydrogen content by about 45% and occlusionby about 55%. The bath temperature prior to treatment was 1620 C. andwas found to be 1595 C. upon completion of treatment.

Example V The general method and apparatus as described in EX- `ample IVwere used, however, with the modification that the steel was not killedduring tapping from the electric furnace, so that the silicon contentwas only 0.07%. In this case, liters of hydrogen per ton of steel wereintroduced through tuyere block 2, as well as 10 liters of car-bonmonoxide per ton of steel through lance 10. Degree of vacuum land lengthof treatment were the same -as described in Example IV.

Initial steel bath temperature was 1615 C. and the .temperature uponcompletion of treatment was 1595 C. It was found that the oxygen contentof the steel had been reduced by about 65%, the hydrogen content byabout 45% and the amount of occlusion by about 65% In Examples IV and V,determination of the oxygen content was carried out by the hotextraction method, determination of the hydrogen content by the tinfusing method and ldetermination of lthe occlusione by separation of theresidue.

Example VI The method of the present invention was `carried lout in anapparatus .as illustrated in FIG. 5.

Liquid steel was treated and finished in an open hearth furnace inconventional manner. Eighty tons of the molten steel were introducedinto container 1 of FIG. 5. The steel composition was as follows:

Percent C 0.30 Si 0.27 Mn 0.50 S 0.034 P 0.021

`of steel. Lance 13 was made ofceramic material andthe introduction ofargon was evenly distributed over the entire treating period of aboutl16 minutes. The lance was placed in such position within container 1that the free lower end of the lance was located about 30 cm. above thebot-tom of container 1.

After completion of the treatment, lance and hood were removed and themolten steel was cast into ingots.

Analysis of the thus treated steel in accordance with the methodsdescribed in connection with Example V, showed that the above treatmenthad reduced the oxygen content of the steel by about 25%, hydrogencontent by about 30% and occlusions by about 30%. The initial bathtemperature was 1620 C. and the temperature upon completion of treatmentwas 1590o C.

Example VII A process somewhat similar to what has been described inExample VI was carried out in the apparatus illustrated in FIG. 6.

Through tuyere block 2, a combustion gas consisting of 40% carbonmonoxide and 60% carbon dioxide was introduced in a quantity `of 28liters per ton of steel.r The temperature of the combustion gas enteringcontainer 1 was about 1450" C. Simultaneously, through lance 12, 15liters of argon per ton of steel were introduced into the molten mass.Treatment was carried out for 12 minutes at a residual pressure of 2mm.rmercury as described in Example VI.

Steel bath temperature prior to treatment was 1610 C. and uponcompletion of treatment 1600 C.

It was found, by using the analytical methods described in Example V,that the oxygen content of the steel had been reduced by about 35% thehydrogen content by about 40% and occlusions by about 40%.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention, that others can, by applying current knowledgereadily adapt it for various applications without omitting featuresthat, from the standpoint of prior art, fairly constitute essentialcharacteristics of the generic or specific aspects of this invention,and, therefore, such adaptations should and are intended to becomprehended within the meaning and range of equivalence of thefollowing claims.

What is claimed as new and desired to be secured by Letters Patent is:

1. In a method of purifying molten steel, the steps of subjecting a massof unkilled molten steel to a partial vacuum; blowing hydrogen gas intothe bottom portion of said mass of unkilled molten steel; andsimultaneously blowing into the interior of said mass of molten steel ata point located above said bottom portion thereof a second gas selectedfrom the group consisting of argon and carbon monoxide while maintainingsaid partial vacuum.

2. In a method of purifying molten steel, the steps of subjecting a massof molten steel to a partial vacuum; blowing first gas into the lowerportion of said mass of molten steel; and simultaneously blowing intothe interior of said mass of molten steel at a point located above saidlower portion thereof a second gas, while maintaining said partialvacuum, one of said first and second gases being an oxidizing gas andthe other being a non-oxidizing gas.

3. In a method of purifying molten steel, the steps of subjecting a massof molten steel to a partial vacuum; blowing first gas into the lowerportion of said mass of molten steel; and continuously blowing into theinterior of said mass of molten steel at a point located above saidlower portion thereof a second gas, while maintaining said partialvacuum, one of said first and second gases being an oxidizing gas andthe other being a reducing gas.

e. In a method of purifying killed molten steel, the steps of subjectinga mass of molten steel to a partial vacuum; blowing a first oxidizinggas into the lower portion of said mass of molten steel; andsimultaneously blowing into the interior of said mass of molten steel ata point located above said Ilower portion thereof a second reducing gas,while maintaining said partial vacuum.

5. In a method of purifying molten steel, the steps of subjecting a massof molten steel to a partial vacuum;

blowing a first reducing gas into the lower portion of said mass ofmolten steel; and simultaneously blowing into the interior of said massof molten steel at a point located above said lower portion thereof asecond inert gas, while maintaining said partial vacuum.

6. In a method of purifying molten steel, the steps of subjecting a massof molten steel to a partial vacuum; blowing a first reducing gas intothe lower portion of said mass of molten steel; and simultaneouslyblowing into the interior of said mass of molten steel at a pointlocated above said lower portion thereof a second gas, consisting atleast partly of gasied halogen and halogen compounds, while maintainingsaid partial vacuum.

7. In a method of purifying molten steel, the steps of subjecting a massof molten steel to a partial vacuum; blowing a first reducing gas intothe lower portion of said mass of molten steel; and simultaneouslyblowing into the interior of said mass of molten steel at a pointlocated above Said lower portion thereof a second gas consisting atleast partly of chlorine, while maintaining said partial vacuum.

8. In a method of purifying molten steel, the steps of subjecting a massof molten steel to a partial vacuum;

lowing a first reducing gas into the lower portion of said mass ofmolten steel; and simultaneously blowing into the interior of said massof molten steel at a point located above said lower portion thereof asecond gas consisting at least partly of fluorine, while maintainingsaid partial vacuum.

9. In a method of purifying molten steel, the steps of subjecting a massof molten steel to a partial vacuum; blowing a first reducing gas intothe lower portion of said mass of molten steel; and simultaneouslyblowing into the interior of said mass of molten steel at a pointlocated above said lower portion thereof a second gas consisting atleast partly of carbon tetrachloride, while maintaining said partialvacuum.

l0. In a method of purifying molten steel, the steps of subjecting amass of molten steel to a partial vacuum; blowing a first reducing gasinto the lower portion of said mass of molten steel; and simultaneouslyblowing into the interior of said mass of molten steel at a pointlocated above said lower portion thereof a second gas consisting atleast partly of aluminum chloride, while maintaining said partialvacuum.

Il. In a method of purifying molten steel, the steps of subjecting amass of molten steel to a partial vacuum;

blowing a rst reducing gas into the lower portion of said mass of moltensteel; and simultaneously blowing into the interior of said mass ofmolten steel at a point located above said lower portion thereof asecond gas consisting at least partly of aluminum fluoride, whilemaintaining said partial vacuum.

12. In a method of purifying molten steel, the steps of subjecting amass of molten steel to a partial vacuum; blowing a first oxidizing gasinto the lower portion of said mass of molten steel; and simultaneouslyblowing through a lance into the interior of said mass of molten steelat a point located above said lower portion thereof a second reducinggas, while maintaining said partial vacuum.

I3. In a method of purifying molten. steel, the steps of subjecting amass of molten steel to a partial vacuum; blowing a mixture of carbondioxide and carbon monoxide into the lower portion of said mass ofmolten steel; and simultaneously blowing into the interior of said massof molten steel at a point located above said lower portion thereofhydrogen gas, while maintaining said partial vacuum.

14. In a method of purifying molten steel, the steps of subjecting amass of molten steel to a partial vacuum; blowing hydrogen gas into thelower portion of said mass of molten steel; and simultaneously blowingcarbon monoxide into the interior of said mass of molten steel at apoint located above said lower portion thereof, while maintaining saidpartial vacuum.

I5. In a method of purifying molten steel, the steps of subjecting amass of molten steel to a partial vacuum; blowing a mixture of carbondioxide and carbon monoxide into the lower portion of said mass ofmolten steel; and simultaneously blowing argon into the interior of saidmass of molten steel at a point located above said lower portionthereof, while maintaining said partial vacuum. Y

References Cited by the Examiner UNITED STATES PATENTS 1,921,060 8/33Williams 75-49 2,817,584 12/57 Iootz 75-60 2,871,008 l/59 Spire 75--59FORElGN PATENTS 3 38,409 11/30 Great Britain.

OTHER REFERENCES Metal Progress, September i959, pp. lll-114.

DAVID L. RECK, Primary Examiner.

1. IN A METHOD OF PURIFYING MOLTEN STEEL, THE STEPS OF SUBJECTING A MASSOF UNKILLED MOLTEN STEEL TO A PARTIAL VACUUM; BLOWING HYDROGEN GAS INTOTHE BOTTOM PORTION OF SAID MASS OF UNKILLED MOLTEN STEEL; ANDSIMULTANEOUSLY BLOWING INTO THE INTERIOR OF SAID MASS OF MOLTEN STEEL ATA POINT LOCATED ABOVE SAID BOTTOM PORTIONTHEREOF A SECOND GAS SELECTEDFROM THE GROUP CONSISTING OF ARGON AND CARBON MONOXIDE WHILE MAINTAININGSAID PARTIAL VACUUM.